I wish I had reported this event immediately. Finally checking the NUFORC log today, I found 3 reports around 5am of May 9 that share elements of my sighting, but I believe that I witnessed a more complete, longer duration event. Returning home after a very late night at work (normal for me), I had just pulled off I-280 at the Foothill College (Moody Rd.) exit when a bright light in the southern sky caught my attention. I am thoroughly familiar with the constellations and celestial bodies, so anything "out of place" is immediately evident. This object was at least Sirius- or Jupiter-bright, in the constellation Ophiuchus and somehwat east of Arcturus. Jupiter had already set or was obscured by the coastal ridge. The object was moving very slowly north- or northwestward and at first I took it to be an incoming aircraft. Expecting its brilliant, steady white light to begin strobing any second, I was astonished when instead it sprouted a "vapor trail" on its left side that mimicked a classic comet tail (I noted the time [5:06] on my car's digital clock about now). This trail was highly structured and almost perfectly triangular. It then began to grow steadily but maintained its geometrical shape. As I continued to watch (I had parked my car on the periphery of Foothill College by this point) it was as though the mass of the original object were being converted into this growing exhaust trail. Eventually, the object was completely "consumed" and no longer visible, leaving behind a glowing elliptical cloud with a very long major axis. This cloud easily covered the area of a small to mid-size constellation, perhaps larger than Ursa Minor or about half of Hydra. It faded gradually but I could still make out traces of it 10 to 15 minutes later when I arrived at home. As far as altitude and location, I would estimate it to be somewhat higher (2000-3000 ft.) and closer to the coast than the San Jose observer. I fully expected some mention of it to be made immediately on local radio (there was nothing subtle about this!), but KGO, KCBS, and KQED-FM were all silent. Nothing could be found in print the next day. I have been intending to check the NUFORC log all this time, but the more usual weirdnesses of life have kept me distracted. By the way, I am a CSETI member and have witnessed a wide range of UFO phenomena, but nothing before quite like this. I am willing to discuss this incident with anyone.